Method of coating steel and product thereof



United States Patent METHOD OF COATING STEEL AND PRODUCT THEREOF Eldon B. Moore, Calumet City, and Elliot S. Nachtman,

Park Forest, 111., assignors to La Salle t lt-eel $0., Hammond, Ind., a corporationof Delaware No Drawin Application June 15, 1955, serial No. 515,794

6 Claims. (Cl. 148-4) This invention relates to the Working of steel as by drawing steel bars, rods, wires or tubes to elfect reduction in cross-sectional area and it relates more specifically to the treatment of steel in working or drawing to improve the surface finish of lthe steel, to reduce the load required to etfect the desired reduction in crosssectional areamand to improve the physical and mechanical properties of the steel.

This application is a continuation-in-part of our copending applicationSen-No. 293,435, filed June 13, 1952, entitled New and lmprovedSteel Products and Methods for Producing Same, now abandoned.

It is an object of this invention to provide a method for improving the surface finish of steel as an incidence to the working of the steel for eifec'ting a reduction in cross-sectional area and it is a" related object to treat the surface of the'steel in advance of working to effect reduction in cross-sectional area with a material that reacts with the conditions existing to produce .a new and improved surface finish on. the steel and which also reduces the load required to .eifect the reduction in crosssectional area.

More specifically, it is an object of this invention to coat the steel prior to working to effect reduction in cross-sectional area, as by advancing the steel in the form of a bar or rod through a draw die, wherein. the coating reacts to produce a bright, shiny and smooth surface layer on the steel and which acts as a lubricant to reduce the load required to eifect the desired reduction in cross-sectional area wherein the'reduction in pull load is greater than heretofore secured by conventional lubricants of the type heretofore employed.

In the aforementioned copending application, of which this is a continuation-in-part; description has been made of a new and improvedgmetallurgical process for producing a bright and shiny surface layer on steel as an incidence to the working of the steel to efiect reduction in cross-sectional area, as by drawing the steel through a draw die. The invention is described with reference to development of the desired results with a non-austenitic steelhaving apearlitic structure in a matrix of free ferrite, but it is believed that the invention in the development of the desired characteristics is available also with other steels and alloy steels.

In accordance-with. the teaching of the aforementioned application, the new and: improved surface finish is developed when the steel, heated to a temperature in excess of 300 F. and preferably to within the range of 3001100 F., is advanced through a draw die to effect reduction in cross-sectional area while coated with molybdenum disulphide prior to such working to effect reduction.

It has now been found that the improvements secured by working the steel at an elevated temperatureto elfect reduction in cross-sectional area with molybdenum disulphide present as a coating on the steel are available also when the steels are coated with other compounds, such for example as cadmium iodide, copper bromide,

"ice

tungsten sulphide, silver sulphate and the like. While these compounds are somewhat unlike molybdenum disulphide and not equivalent thereto in the general sense, it appears that these other compounds have a similar layer, lattice-type structure as molybdenum disulphide which enables reaction on the steel under the pressure and temperature conditions existing in the draw'die to produce a finish which is similar in appearance and structure but of necessity different in composition than that secured with molybdenum disulphide.

It has been found further that the presence of molybdenum disulphide or the other compounds on the surfaces of the steel results also in a marked reduction in the load required to effect the desired reduction in cross-sectional area of the steel. As such the molybdenum disulphide and other compounds function additionally as a lubricant for the steel when processed through a metal draw die or otherwise worked to effect reduction in cross-sectional area. Reduction in pull load is particularly effective with the use of molybdenum disulphide when the steel drawn is heated to a temperature in excess of 300 F. and preferably within the range of 3001l00 F.

The invention herein will be described with particular reference to the-use of molybdenum disulphide as the substance applied, preferably in the form of a drypowder, to the surface of the steel for reaction to develop the desired results underthe temperature and pressure conditions existing, but it will be understood that the other compounds having a layer, lattice-type structure, such as previously'named, may also be used:

The molybdenum disulphide reacts on the steel surface differently thannother metal salts which might previous- -ly have been used as metal lubricants, such for example as lead sulphide. The difference betweenmclybdenum disulphide and lead sulphide, for example, is particularly noticeable from the standpoint of appearance which each imparts tothe finished steel as it emerges from the draw die and afterwards and the difference'is also noticeable from the standpoint of pull loads in pounds required to effect equivalent reductions in similar steels under similar conditions, especially in drawing steel heated to an elevatedternperature in excess of 300 F. Differences are also noticeable from the standpoint of the finish which is secured on the steel by way of surface smoothness and the other characteristics of the drawn steel.

The amount of molybdenum disulphide applied to the surface of thesteel is not critical as long as an amount of molybdenum disulphide is present on the surface sufiicient to form a substantially continuous monomolecular film comprised of the reaction product that is formed between the molybdenum disulphide and the steel at the surface. An excess of molybdenum', disulphide may be presentonvthe steel but the depth of the new and improved surface layer having abright metallic and silver-like finish is not substantially increased and therefore the presence of such excesses are of no apparent value.

When processed in accordance with the practice of this invention, the steel issuing from the draw die is characterized by having a smooth and permanent bright metal finish. The surface appears to be highly resistant to deterioration, dulling or attack by elements normally existing in the atmosphere. It is possible by taking abnormally heavy drafts with appropriate die practice, to produce an improved surface without heating the metal to an elevated temperature. However, the unexpected reductions in drawing load are secured mainly when drawing with molybdenum disulphide on the surface of the steel which has been heated to an elevated temperature in excess of 300 F. Whencompared directly to lead sulphide or to sodium bismuthate and the like, the molybdenum disulphide present on the surface of the steel is Two austenitic steels having the following composition were subjected to a series of identical processing steps:

Material Mn P S Si The following is the procedure which was used for making the comparison:

inch diameter bars of C-l018 and (3-1144 steels were drawn at inch draft to a inch diameter (1) at room temperature after the prescribed lubricant had been applied dry; (2) at 400 F. with the lubricant applied dry (a) before heating and (b) after heating but before drawing. The steel was drawn at the rate of 25 feet per minute.

The results which were secured with the two different steels drawn under the described conditions are tabulated as follows:

of other materials conventionally employed as lubricants or for surface treatment. This reaction not only results in reduced friction between the die and metal drawn but also produces a plate-like deposit which is quite unlike any deposit heretofore observable. By the use of appropriate pressures and temperatures, the layer structure is produced which is strongly adherent and appears to be an integral part of the surface of the drawn steel part.

Because of the reaction which appears to take place to form a smooth surface on the steel in the draw die or for whatever other unknown reasons or reaction, it has been found that the pull load required to effect a reduction in cross-sectional area is less in the use of molybdenum disulphide than for other lubricants especially when operating on steel heated to an elevated temperature.

By comparison with conventional lubricants, the pull load with molybdenum disulphide was less in every instance than the pull load with other materials at the same temperature, with the same steels, at the same amount of reduction. For example, the pull load with molybdenum disulphide at 500 F. was as much as percent less than the pull load required with a similar reduction with the same steel and effected with lead sulphide, and the pull load with molybdenum disluphide was never more than 25 percent less than the pull load for lead sulphide.

The following example will illustrate the improvements which are secured in appearance of the steels drawn at various temperatures ranging from room temperatures up to about the lower critical temperature for the steel composition:

DRAWING AT ROOM TEMPERATURE Lubricant Average Average Pull in Appearance Pull in Appearance Pounds Pounds Molybdenum dlsulphidenn 8, 590 Chrome-like bright metallie 10, 845 Chrome'like bright metallic. Lead sulphide 9, 735 Mottled gray 13, 755 Mottled gray. Antimony sulphide 8, 590 do 10, 845 Do. Sodium bismuthate- 9, 735 Orange gray 13, 300 Orange gray. Nox-Rust 8, 025 Mottled gray 10, 845 Mottled gray.

DRAWING LUBRIOATED STEEL AT 400F.

Molybdenum disulphide 6. 015 Chrome-like bright metallic-.. 8, 690 Chrome-like bright metallic. Lead sulphide 8, 690 Mottled gray 12,685 Mottled gray. Antimony sulphide. 9, 165 do 8,590 Do. Sodium bismuthate- 8, 020 Orange gray 10, 270 Orange gray.

DRAWING AT 400 F. WITH LUBRICANT APPLIED AFTER HEATING Molybdenum disulphide 6, 685 Ohrome'like bright metallic... 9, 735 Chrome-like bright metallic. Lead sulphide 13, 755 Mottled gra 15, 450 Mottled gray. Antimony sulphide Broke La ck of proper Lubrication Sodium bismuthate. 9, 735 Orange gray. Nox-Rust 8, 595 Mottled gray.

The surface appearance of a drawn steel bar represents an important consideration which controls the selection of a lubricant because it is desirable to have the surface of the drawn bar free of defects not only from hot mill rolling, such as laps and scams, but also free of scratches and gauling due to lack of lubrication or from improper lubrication. From the data which has been developed as set forth in the foregoing tables, it will be seen that steels drawn with molybdenum disulphide as a lubricant are characterized by having a bright, shiny, smooth metallic surface approaching a chrome-like appearance when compared with the relatively dull, mottled gray appearance visible on the surfaces of the same steels drawn with other lubricants such as lead sulphide, sodium bismuthate, antimony sulphide, and conventional oil base lubricants.

A distinctively different reaction occurs in the use of molybdenum disulphide as the material on the surface of the steel to be drawn as distinguished from the presence EXAMPLE 2 The following data was developed with steel having the following composition:

0.48 percent carbon 1.50 percent manganese 0.03 percent phosphorus 0.27 percent sulphur 0.30 percent silicon 0.005 percent nitrogen form a new compound of or reduce -the compound to molybdenum metal or an alloy thereofwith the steelbutiuany event,the new substance is stronglyanchored and=embeddedin the surface of the drawn steel to-become a permanent part thereof.

itis believed thatth-is is the" first time that molybdenum Efiect of drawing at elevated temperatures on surface-finish il "l 75 300 500 "700 .900" L200 Surface Finish in Mieroin'chcs. 20 30.-" 20 :6 .10 10. Surface Appearance Matte... semi'bright" chromebright. ,chrome bright- .chrome bright. Matte.

It will be apparent from the foregoing that the nonaustenitic steels having a pearlitic structure in a matrix of free ferrite permit the use of molybdenum disulphide as a drawing lubricant for steels and that when the steel is drawn through the die at elevated temperatures between 300 and 1100 F., marked reduction in surface roughness and a bright surface finish are substantially permanently formed on the surface of the drawn metal thereby to improve the appearance and characteristics of the steel and eliminate the additional steps heretofore required to obtain a surface finish and to protect the finish from attack or deterioration.

The method of heating to raise the steel to the desired temperature levels for drawing is unimportant. Use is made of conventional means such as an oil bath, gas fired furnace, electrical heating means or the like. In the event that the technique described and claimed in the copending application of Elliot S. Nachtman, Ser. No. 286,039, filed May 3, 1952, now abandoned, is employed to prepare the steel surface for drawing, as by the application or treatment with molten salts, temperature of the desired level may be introduced by the molten salts and the molybdenum disulphide embodied as an ingredient therein to produce the desired finish on the steel surface. It is preferred, however, to apply the molybdenum disulphide in accordance with the practice herein subsequent to the salt treatment, with or Without the removal thereof.

EXAMPLE 3 Steel composition:

0.17 percent carbon 0.75 percent manganese 0.03 percent phosphorus 0.04 percent sulphur 0.08 percent silicon 0.005 percent nitrogen /8 inch hot rolled steel of the above composition, which is a steel of the non-austenitic type having a pearlitic structure in a matrix of free ferrite, was heated to a temperature of 900 F. in a gas fired furnace and advanced continuously through a drawing die to secure a 19 percent reduction in cross-sectional area. One group of bars were drawn through the die With a normal oil base lubricant applied to the surface thereof while another group were coated in advance of passage through the die with molybdenum disulphide dispersed in 5-10 percent concentrations in a grease composition.

The surface finish on the drawn steel not having molybdenum disulphide applied to the surface thereof was matted and dulled and required a subsequent grinding operation to increase its luster and then had to be wrapped in a special treated paper to protect the surface finish against rusting or deterioration by elements normally existing in the atmosphere. On the other hand, the surface finish on the steel drawn through the die under the same conditions but with molybdenum disulphide on the surface thereof had the appearance of bright chrome and resisted deterioration or attack. For all practical purposes, it appears as though the salt had been reacted .under the heat and pressure existing in the draw die to disulphide has beenused to pro'duce-ai bright --and protective surface of this character on steel. It is believed that this is the first time that molybdenum disulphide has been used to reduce the pull load required to draw steel through a draw die to effect reduction in cross-sectional area.

It will be apparent from the foregoing that the combination of pressure and temperatures available during drawing steel to effect reduction in cross-sectional area provide conditions by which these new and desirable results are developed. Reaction sufficient to develop an improved surface finish on the steel may be secured by the use of molybdenum disulphide without preheating the metal to an elevated temperature but the brightness is not as good as that secured with steel heated to an elevated temperature. The pull load is also reduced by the use of molybdenum disulphide as a lubricant when compared with the use of other salts such as lead sulphide, sodium bismuthate and the like to lubricate the surface of steel in a drawing operation.

As used herein, the term surface roughness is an indication of the smoothness of the formed surface taken by a profilometer readable in terms of micro inches.

It will be understood that the use of molybdenum disulphide or other compounds having a layer-lattice-type structure such as cadmium iodide, copper bromide, tungsten sulphide and silver sulphate as a lubricant and as a material to develop improved surface characteristics on metal and to reduce drawing loads is not limited to use with non-austenitic steels of the type described. It is believed that the application of molybdenum disulphide as a lubricant and as a surface treating composition concurrently to improve the character of the surface finish and reduce pull load is applicable to other steels and alloys of steel and that such other uses may be made without departing from the spirit of the invention, especially as defined in the following claims.

We claim:

1. The method of treating steel to produce a smooth surface layer of improved brightness comprising working the steel to effect a reduction in cross sectional area at a temperature above 300 F. but below the lower critical temperature for the steel composition and with a coating of molybdenum dispulphide on the surface thereof.

2. The method of processing steel of the non-austenitic type having a pearlitic structure in a matrix of free ferrite to improve the characteristics thereof comprising the steps of drawing the steel through a drawing die while the steel is heated to a temperature within the range of 3001100 F. and with a coating of molybednum disulphide on the surface thereof.

3. The method of processing steel of the non-austeuitic type to improve the characteristics thereof comprising the steps of heating the steel in a solid integral mass to a temperature above 300 F. but below the lower critical temperature for the steel composition, coating the heated steel with molybdenum disulphide and then Working the coated and heated steel at a temperature above 300 F. whereby reaction takes place to form a bright and permanent metal finish on the steel surface.

the molybdenum disulphide 4. The method of processing steel of the non-austenitic type comprising the steps of heating the steel to a temperature above 300 F. but below the lower critical temperature for the steel composition, coating the steel surface with molybdenum disulphide and then drawing the steel through a drawing die to effect reduction in cross sectional area while heated to the elevated temperature.

5. The method of processing steel of the non-austenitic type comprising the steps of heating the steel in advance of drawing to a temperature between 300 and 1100 F., applying a molybdenum disulphide powder to the surface of the heated steel and then drawing the steel through a drawing die to effect reduction in cross sectional area while heated to the elevated temperature.

6. The method of processing steel of the non-austenitic type comprising the steps of coating the steel in advance of drawing with a composition containing molyb- References Cited in the file of this patent UNITED STATES PATENTS 2,280,886 Brace Apr. 28, 1942 2,361,211 Zimmer Oct. 24, 1944 2,400,866 Kronwall May 21, 1946 2,588,234 Henricks Mar. 4, 1952 OTHER REFERENCES Alloy Metals Review, vol. 7, No. 51, March 1949 (pp. 2-8). 

1. THE METHOD OF TREATING STEEL TO PRODUCE A SMOOTH SURFACE LAYER OF IMPROVED BRIGHTNESS COMPRISING WORKING THE STEEL TO EFFECT A REDUCTION IN CROSS SECTIONAL AREA AT A TEMPERATURE ABOVE 300*F. BUT BELOW THE LOWER CRITICAL TEMPERATURE FOR THE STEEL COMPOSITION AND WITH A COATING OF MOLYBDENUM DISPULPHIDE ON THE SURFACE THEREOF. 